The discussion revolves around the concept of electron affinity (E.A.) for elements in periods 2 and 3 of the periodic table. Participants explore why E.A. is negative, how it varies across periods and groups, and the specific cases of fluorine and chlorine.
Participants express differing views on the electron affinities of fluorine and chlorine, with some asserting that fluorine has a greater E.A. while others argue the opposite. The discussion remains unresolved regarding the comparison of E.A. between these two elements.
Participants reference specific numerical values for electron affinities of chlorine, bromine, and iodine, but the implications of these values are debated. The discussion includes assumptions about atomic size and electron density that are not fully resolved.
Kushal said:period 3 elements have SMALLER electron affinities than period 2 elements for the reasons above. But an exception is F(period 2) and Cl(period 3). This is due to the fact that F has a very small size...
Hope i helped you
ritwik06 said:Why is electron affinity negative?
In my book its written, that on moving down a group, tit decreases. But why is it that period 3 elements have greater E.A. than period 2 elements?
Kushal said:you should precise which E.A.! The first E.A. is the amount of energy released when 1 mol of a gaseous atom accepts 1 mol electrons. the first E.A. is always negative. E.A. is in fact an energy change; when an energy change is -ve, it implies that the reaction is exothermic, i.e energy is liberated...and when energy change is +ve, it implies that the reaction is endothermic, i.e energy is absorbed. right
the attraction between the nucleus and the first electron to be accepted releases energy. the second E.A. and succeeding ones are all endothermic. this is because energy is needed to force the electron into the atom. energy is now required as the second incoming electron is being at the same time attracted by the nucleus and repelled(to a larger extent) by the other electrons of the atom. right
E.A. decreases down a group. this is because, down a group the atoms become shielded by the larger numbers of electrons. (e.g. Li has 3 e-, Na has 11e-, K has 19e-,...) the shielding decreases the attractive force of the nucleus on the incoming electron and furthermore, the incoming electron is being repelled at a greater extent by the larger number of electrons. i.e more energy is required to force that electron into the atom.
period 3 elements have SMALLER electron affinities than period 2 elements for the reasons above. But an exception is F(period 2) and Cl(period 3). This is due to the fact that F has a very small size...
Hope i helped you
TripleS said:how is that an exception?...doesnt F have a greater E.A than Cl?
Nope. Though F is more electronegative than Cl, E.A of F is less than Cl. It is because F is comparatively very small atom which give it higher electron density than it's neighbours. If you want to place an electron in it's (F)outermost shell you have to do some extra work (for the extra density of electrons it has). So overall it effects the net realease of energy.